The present invention claims the benefit of the Korean Patent Application No. P2003-99241, filed in Korea on Dec. 29, 2003, which is hereby incorporated by reference.
1. Field of the Invention
The present invention relates to an organic electroluminescent device, and more particularly, to an organic electroluminescent display device that includes first and second array substrates and at least one spacer, and a method of fabricating the same.
2. Discussion of the Related Art
In recent times, various flat panel display technologies have been developed resulting in the display device having an overall reduced bulk and weight. Display devices utilizing these flat panel display technologies are free from the disadvantages of prior technologies that utilized a typically bulky and heavy cathode ray tube (CRT) to generate the display. Such flat panel display technologies can be of various types, including a liquid crystal display (LCD), a field emission display (FED), a plasma display panel (PDP), and an electroluminescent (EL) display device.
Among these various flat panel display types, the structure and fabrication process of the PDP is relatively simple, resulting in the PDP display type being particularly advantageous for light-weight, large-sized applications. However, the light emission efficiency and brightness level of such PDPs are relatively low. At the same time, such PDP devices typically consume a large amount of power.
In comparison, LCD technology, which utilizes a thin film transistor (TFT) as a switching device, is not preferred for large-sized applications because it is fabricated by a relatively-complex semiconductor process. Nevertheless, the demand for LCD technology continues to increase for relatively small display applications, such as in notebook computer displays. However, particular disadvantages of LCD technology include its high power consumption, its difficulty to be made large-sized, and its inclusion of a backlight unit as a light source. Further, LCD arrangements result in a high amount of optical loss that results from its utilization of optical devices such as a polarizing filter, a prism sheet and a diffusion panel. Moreover, the viewing angle of such LCD arrangements is narrow, as compared to other display types.
As compared with LCD technology, EL display devices are generally classified into two types: inorganic EL devices and organic EL devices, based on the material making up its light-emission layer. A spontaneous light-emitting EL display device has an advantage over other flat panel display types in that it has a fast response speed, a high light-emission efficiency, and a superior brightness level. Moreover, EL display devices are advantageous in that they have a wide viewing angle.
The organic EL display device, as shown in FIG. 1, includes sub pixels 50 wherein each sub pixel is arranged at the intersection area of a gate line GL and a data line DL. Each sub pixel 50 receives a data signal from the data line DL and generates light corresponding to the data signal when a gate pulse is applied to the gate line GL.
In this regard, the sub pixel 50 includes an EL cell OEL having a cathode connected to a ground voltage source GND. The sub pixel 50 also includes a cell driver 52 connected to the gate line GL, the data line DL and a supply voltage source VDD. The cell driver 52 is also connected to the anode of the EL cell OEL for driving the EL cell OEL. The cell driver 52 includes a switching thin film transistor T1, a driving thin film transistor T2, and a capacitor C.
When a scan pulse is applied to the gate line GL, the switching thin film transistor T1 is turned-on and it supplies a data signal from the data line DL to a node N. The data signal supplied to the node N is charged in the capacitor C. Simultaneously the data signal is applied to a gate terminal of the driving thin film transistor T2. The driving thin film transistor T2 controls the amount of current I applied to the EL cell OEL from the supply voltage source VDD in response to the data signal supplied to the gate terminal to thereby control the amount of light emission of the EL cell OEL. As a result, even though the switching thin film transistor T1 may be turned off, since the data signal is discharged from the capacitor C, the driving thin film transistor T2 continues to supply current I from the supply voltage source VDD to the EL cell OEL until the data signal of the next frame is applied. This results in the EL cell OEL light emission being sustained.
FIG. 2 is a sectional view representing a pixel of the organic EL as shown in FIG. 1 in which the pixel includes red, green and blue sub pixels to form one pixel region. The EL display, as shown in FIG. 2, includes a substrate 2 and a packaging plate 12, which are combined by a sealant 18. A plurality of EL cells are formed within a display region arranged by the sealant 18 on the substrate 2. Each of these EL cells includes an organic layer formed between an anode electrode 4 and a cathode electrode 6, which cross each other and are insulated from each other.
Each anode electrode 4 is separated by a predetermined distance from other anode electrodes on the substrate 2. A first driving signal is supplied through the driving thin film transistor T2 to the anode electrode 4 to emit holes from the anode electrode 4.
The organic layer 10 includes a hole carrier layer 10a which carries holes emitted from the anode electrode 4 to a light-emitting layer 10b. The light-emitting layer 10b generates visible light by a combination of the holes and electrons emitted from the cathode electrode 6. An electron carrier layer 10c carries the electrons to a light-emitting layer 10b. 
The cathode electrode 6 is separated from other cathode electrodes by a predetermined distance on the organic layer 10 and is formed crossing the anode electrode 4. Furthermore, a second driving signal is supplied to the cathode electrode 6 to emit the electrons.
The packaging plate 12, made up of a metallic material, includes an oxygen and moisture absorbent material. The packaging plate 12 serves to radiate heat that is generated upon the light-emission of the organic layer 10. The packaging plate 12 also serves to protect the organic layer 10 from external forces, as well as from moisture and oxygen in the atmosphere.
If a driving signal is applied to the anode electrode 4 and the cathode electrode 6 in the organic EL display device, the electrons and the holes are emitted and then re-combined to generate visible light from the organic layer 10. At this time, the visible light exits to the exterior via the anode electrode 4 and the substrate 2, where it is used to display a picture or image.
FIG. 3 is a flow diagram representing a manufacturing process of the related art organic EL display device. At step S11, a signal line including a gate line, a data line and a supply line, and a thin film transistor array including a driving thin film transistor and a switching thin film transistor are formed on the substrate. At step S12, an anode electrode is formed to connect to a drain electrode of the driving thin film transistor. At step S13, an organic layer including a hole carrier layer, a light-emitting layer and electron carrier layer is formed on the anode electrode. At step S14, a cathode electrode intersecting with the anode electrode is formed on the organic layer. Then, at step S15, a packaging plate is combined with the substrate by a sealant in order to protect the substrate having the thin film transistor array, the anode electrode, the organic layer and the cathode electrode formed thereon.
As described above, the related art organic EL display device is made by combining the packaging plate with the substrate having the thin film transistor and the organic light-emitting layer. In such an arrangement, the overall organic EL display device's production yield is determined based on both the production yield of the thin film transistor and the production yield of the organic layer. Particularly, the production yield of the organic EL display device is determined depending on the production yield of the organic layer, which has a high defective rate, especially when compared to the thin film transistor's defective rate. For instance, even though a thin film transistor formed on the substrate has a good quality and acceptable production yield, the overall organic EL display device can be regarded as defective as a result of a poor production yield associated with the organic layer having a thin film of about 1000 Å in thickness. Therefore, this results in a problem with such related art arrangements in that the costs of raw materials and other expenses associated with manufacturing a thin film transistor of good quality are sacrificed, while the overall device production yield is lowered.
Moreover, the related art organic EL display device is a lower portion light-emitting type in which the visible light rays exit to the exterior via the rear surface of the substrate. While this arrangement of the related art organic EL display device results in a high stability and a desirable degree of freedom of processing by the packaging plate, it also suffers from a particular difficulty to adapt to high-resolution applications.